Gas turbine engines generally include a combustor with a number of fuel nozzles positioned therein in various configurations. For example, a DLN2.6+ (“Dry Low NOx”) combustion system offered by General Electric Corporation of Schenectady, N.Y. provides a six fuel nozzle configuration with a center fuel nozzle surrounded by five outer fuel nozzles. Such a combustion system mixes one or more fuel streams and air streams before entry into a reaction or a combustion zone. Such premixing tends to reduce overall combustion temperatures as well as undesirable emissions such as nitrogen oxides (NOx).
As is known, the fuel nozzles generally include a number of fuel and air tubes mounted onto a flange. In the DLN2.6+ combustion system, the fuel nozzles may be positioned within a cap assembly in a somewhat cantilevered fashion. The combination of the cantilevered structure and the natural frequency of the center fuel nozzles, however, have caused somewhat high amplitude resonance that has resulted in issues with respect to a braised joint between the flange and one of the outer premixed tubes.
Although the design of the fuel nozzle and the cap assembly may be revised to eliminate the issue with the joint, there is a considerable amount of equipment currently operating in the field. There is a desire therefore for systems and methods to dampen or at least to shift the natural frequency of the center fuel tube so as to avoid any issues that may arise with high amplitude resonance. The systems and methods preferably can dampen or shift the natural frequency of the fuel nozzle without extensive equipment replacement or modification costs.